O, o&#39;-dialkyl s (alkyl sulfoxyethyl) phosphorothiolates as pesticides



0, '-DIALKYL S(ALKYL SULFOXYETHYL) PHOS- PHOROTHIOLATES AS PESTICIDES David William John Lane, Cambridge, and Dennis Frederick Heath, Hauxton, England, assignors to Pest Control Limited, Bourn, England, a British company No Drawing. Application December 24, 1953, Serial No. 400,364

Claims priority, application Great Britain December 31, 1952 9 Claims. (Cl. 260-461) This invention relates to a new class of organic derivatives of thiophosphoric acid, their manufacture and use.

The invention provides new chemical compounds being sulphoxides of the general formula:

RO S(0 H4)- S -R where R, R and R" are each an alkyl group containing not more than four carbon atoms. Preferably R, R and R" in the general formula each contain not more than three carbon atoms.

The new compounds have systemic pesticidal properties and the invention, therefore, also provides new pesticides consisting of or containing a new compound as defined above and, if desired, also a solid or liquid diluent or solvent.

The new compounds are miscible with water in all proportions and are reasonably stable in it. The preferred diluent is therefore water. Useful spray concentrations may contain e. g. between 0.01 and 0.5% active ingredient. Stock solutions for storage may, of course, contain any desired amount of active ingredient. It is desirable to add a wetting agent in order to ensure that the pesticidal solution spreads evenly on the plant leaves.

Suitable wetting agents which may be used alone or in combination are:

Lissapol NX, a product of Imperial Chemical Industries Limited containing an alkylated phenol-polyethylene oxide condensate;

Triton X-100," a product of Rohm & Haas containing isooctylphenol-polyethylene oxide condensate;

Alcopol 0, a product of Allied Colloids containing di-octyl sodium sulphosuccinate.

The proportion of wetting agent to active ingredient in such compositions may vary within wide limits and may be in some cases as high as 1:1.

Liquid formulations may also be made with organic solvents, such as acetone, benzene, chlorinated hydrocarbons and alcohol, and may contain an emulsifier. Fumigants, such as ethylene dibromide or 1.2-dichloropropane, may also be used as constituents of such liquid formulations.

Solid mixtures may be made by allowing the active ingredient to be adsorbed on inert finely divided mineral or cellulosic materials, such as china clay, fullers earth, bentonite, talc powder and wood flour.

The new compounds have advantages as pesticides over the corresponding compounds (RO)(R'O)P(O)S(C2H4)SR" from which they may be prepared as described below. The new compounds have no smell; they have a lower vapour pressure, so that there is less danger from their vapour and less is lost by evaporation when they are applied to plants; they are soluble in water, which facilitates the preparation of pesticide compositions.

:1 The following are examples of the new compounds:

Compound A.This is 0,0-diethyl-S-(ethylsulphinyl)-' ethyl thiophosphate,

This compound is a colourless Oil which has the following physical properties:

Compound B.This is 0,0-dimethyl-S-(methylsulphinyl)-ethyl thiophosphate,

(CH3O)2P(O).S.(C2Hi).S(O).CHx It is a pale brown liquid of the following physical properties:

Hydrolysis rate in alkaline solution=23i3 (OH-) min.- at 25.4" C. a Partition ratio CHCl Water =1.25i0.05 at 18 C.

Miscible with water and chloroform in all proportions.

Compound C.- This is 0,0 dimethyl S (ethylsulphinyl)-ethyl thiophosphate,

It is a pale brown liquid of the following physical properties:

Partition ratio Hydrolysis rate in alkaline so1ution=20 (OH-) min."

at 25.4 C. Miscible with water and chloroformin all proportions.

CHCI

The reasons for assigning the above formulae to the new compounds are discussed further below.

According to the invention the new compounds are produced from thioethers (R0)(R'O)P(O)S(C2H4)SR", where R, R and R" have the above-defined meanings, by oxidising these compounds with aqueous hydrogen peroxide under neutral conditions at not more than moderately elevated temperature. The reaction may be carried out with or without a solvent, which may be water or. any solvent with which hydrogen peroxide does. not react appreciably but which will dissolve it when vit is added in aqueous solution. We have found that the reaction proceeds smoothly and with yields up. to 97% of the theoretical even 'when using only, the theoretical amount or a very small excess ofhydr ogenperoxide. The concentrations and proportions of hydrogen perozt ide in the reaction mixture and the reaction temperatures may be varied over a wide range, having regard, however, to the instability of hydrogen peroxide on heating and to the increase in reaction speed with rising concentrations of hydrogen peroxide; with concentrated'hydrogen peroxide the reaction becomes violent and uncontrollable when the reactants are present in more than minute quantities.

In carrying out the oxidation the following should be borne in mind:

(a) The hydrogen peroxide cannot be too dilute or the temperature too low, except that at low temperatures and high dilutions the reaction is very slow;

(b) Up to 100 vol. hydrogen peroxide may be used, but care must be taken or the reaction gets out of hand;

A considerable excess even of 100 vol. hydrogen peroxide can be used providing the reaction is stopped by cooling as soon as the temperature no longer rises on removing the cooling bath, and the maximum temperature does not exceed about 85 C.;

(11) If any of the new compounds are heated to 100 C. for five minutes with an equal volume of 100 vol. hydrogen peroxide, further reaction takes place, leading to a mixture of further oxidation products;

(e) If one gm. (CzHO)2P(O)S(C2H4)SC2H5 is heated'to 100 C.. with 1.5 ml. or more of hydrogen peroxide 100 vol. for five minutes at, 100 C., the. main product of reaction is not Compound A but a mixture of further oxidation products.

The following examples will illustrate the production of the new compounds. In order easily to estimate the yield, we used as starting material a compound containing P; the radio-active isotope of phosphorus, which allowed us to determine the partition between various pairs of solvents of the product obtained by measuring the radio activity:

EXAMPLE 1 100 mls. of a 0.212% solution of (CzHsO) 2.P(O) .S.( C2H4) .SCzHs in water were mixed with 20 mls. of 8 vol. hydrogen peroxide (twenty times the theoretical quantity) in water and thermostated at 25.4 C. Aliquots were extracted and analysed for the desired product at the stated intervals by the method given above.

Fraction of starting material converted to Compound A:

30 mins 0.47 60 mins 0.69 3 hour 0.95

EXAMPLE 2 Percent Compound A 93.5 Starting material 6 Ionic compo 0.5

4 EXAMPLE 3 11 gm. of the same starting material as in Example 1 were stirred on a water bath at 70 C. and 20 ml. of 50 vol. hydrogen peroxide (about 100% excess over the theoretical quantity) were added steadily over five minutes. The product was cooled;

Percent Compound A 97 Starting material 2 ionic produ 1 EXAMPLE 4 EXAMPLE 5 To 4 gm. of (CH3O)2P(O)S(C2H4)SC2Hs in a small flask 4 ml. of 100 vol. hydrogen peroxide were addeddrop-wise until the, temperature: rose. The-mixture was cooled to maintain the temperature at 70-80 C. until reaction was complete. The mixture was then diluted with water and washed with benzene once, extracted with chloroform six times and chloroform removed by evaporation under suction.

Yield, by radiotracer assay, 91% of Compound C.

Product-pale brown liquid, still containing atraceof solvent, decomposed by vacuum distillationor molecular. distillation at 100C.

Properties:

Partition ratio Hydrolysis rate in alkaline solution=20 (OH)- min.

at 25 .4 C. Miscible with water and chloroform in all proportions.

EXAMPLE 6 Example 5 was repeated, but using 4 gm. of

(CH3O)2P(O)S(C2H4)SCH3 as starting material.

Yield: of Compound B.

Product: Pale brown liquid, still containing some solvent. Decomposed by vacuum distillation or molecular distillation at C.

Properties:

Hydrolysis rate in alkaline solution= 2 3i3 (QH') min.- at 25.4 C. Partition ratio w 0 water -l.25;l;0.05 at 18 C.

Miscible with water and chloroform in all proportions.

procedures and theoretical vacuum. The product was a colourless oily liquid, which decomposed on attempted fractionation, but distilled slowly in a molecular still under 0.05 mm. Hg pressure with a liquid temperature of 100 C.

The product seemed to be homogeneous and to consist only of one compound. This has been shown in the fol-' creases the alkalinehydrolysis'rate several hundredfold; as does' the"substitution"of'-F for *-'O--CeH4'-NO2 in .r CZHtO P iLO-NO,

The substitution of .SOC2H4S C2H5 for SC2H4SC2H5 in lowing ways, using Compound A derived fromradioactive PCla (phosphorus trichloride containing the radio- 1 active isotope of phosphorus, P).

1. A partition chromatographic column was prepared from gm. kieselguhr (Hyflo-Supercel), 14 gm. of water (static phase) and benzene (eluting phase). A few gms. of the product were placed on the top of the column, which was eluted with benzene. The eluent fractions were assayed for radio-active phosphorus. More than 99.5% of the phosphorus placed on the column appeared in one narrow band.

2. Successive extraction of a very dilute aqueous solu- (I) is a substitution of the same type. The change inthe hydrolysis rate seems, therefore, too slight to be consistent with Compound A being (III), but is consistent with (II), when the'eifectiof the central -SO group would be much .reduced'by. the intervening carbon chain.

1 In confirmation of this reasoning, drastic oxidation of Compound A with a large excess of hydrogen peroxide at 100 C. yields a compound which gives. an infra-red spectrum' consistent with a central structure This compound, is, over one hundred times less stable Llewellyn, Journal Science of Food and Agriculture, 3,1.

68 (1952), Studies on Commercial Octamethylpyrophosphoramide, Part IV) revealed no changes in parti tion ratio as the extraction proceeded. This procedure is the equivalent of countercurrentextraction, a well-, known method of separation.

3. The rate constantfor the hydrolysis rate of a sample of Compound A in a large excess of very dilute alkali showed no drift as hydrolysis proceeded until at least 80% of the compound was hydrolysed. Beyond this deviations do not exceed the experimental error;

The interpretation of these three points is that either Compound A is a mixture of compounds which cannotbe separated by partition chromatography-using very different eluting solvents (benzene and trichloroethylene) and which have very similar hydrolysis rates in alkaline solution, or Compound A is one pure compound. The latter is much more probable.

Compound A can be prepared in good yield by the action of very dilute hydrogen peroxide on in neutral solution. It is general chemical knowledge that under these conditions C-C-H systems are :not attacked, but that CSC systems may be, with the formation of a sulphoxide or sulphone. Onlyone mol.

than (I) to alkaline hydrolysis. Thus a neighbouring highlyelectrophilic group in this system confers the exp cted instabil y tod u qalkalie f .j

Secondly, (I) is very sparingly soluble in water. This low solubility is presumably due to the long hydrophobic -SC2H4SC2H5 .chain.- It is unlikely thatoxidation of the.sulphur adjacent. to the phosphorus would produce 1 a compound which is miscible with water, in all proportions as is Compound A, as the length of the inert, chain is only reduced by one unit in. this way. If, however, the centre sulphur is oxidised to a hydrophilic -SO group then'the observed .charige in solubility is tdb expectedr '0 .The compound is, therefore, believedto be (II).

Similarco'risideratiohsin the case of Compounds B and C lead to the conclusion that the new compounds of the invention have the constitution (I) so of hydrogen peroxide is required to'form one rnol. of.

Compound A from one mol. of (I), therefore the compound is a sulphoxide. It is, therefore, one of the two There are good theoretical grounds for preferring (II) to (HI).

Thus, the hydrolysis rate in alkalies is 3.34 (OH-) min? against 0.81 (OH-) min.- for (I). The. rates are, therefore, similar. It has been shown by a number of workers that the substitution on the phosphorus of one group by a more electrophilic group greatly increases the rate of alkaline hydrolysis, e. g. the substitution of one C2H50- for one (CH3)2N in [(CH3)2N]4P203 in- The newcornpounds are potent systemic insecticides, that is to say are readily absorbed into the sap stream of the living plant by the leaves and transported inside the plant with the sap.

Chrysanthemum leaves, weighing between mgm. and 200 mgm, each, and infested on the lower surface with Coloradoa rufomaculata were treated with 0.1 ml. of a 0.1% solutionof Compound A, which was applied to the upper surface from a pipette. The leaves were then dried and put into Petri dishes on moist filter papers. Aftertwenty four hours, 36.9% of the aphids present were dead. The temperaturewas 20 C.

In another test, lengths of chive leaf, 1 inch long, were filled with 0.1 ml. of a 0.01% solution of Compound A a and sealed with wax at both ends. Seventeen hours after treatment the leaves were put into 2" x A glass tubes and infested with Myzus ascalonicus, the shallot aphid. The temperature was 20 C. After 4 /2 hours, 27.7% of the aphids were dead, and after seven hours 61.1%.

. In the following tables a comparison is made of the biological action of the new Compounds A, B and C of the invention and the known compound (I) from which A is prepared: 7

1 Table I Field bean seedlings, 2 3" high, with two to three bifoliate leaves, were treated either by spraying with insecticide solutions or by pouring 10.ml."solution on to the soil. ,The plantswere infested, at intervals after spraying, with Acyrthosiphon'pisum and Megoura viciae. Three replicate plants for each treatment, 50 to 100 insects for each treatment. A

PLANTS SPRAYED Period of Concen- Interval Percentage Mortalities exposure tratiou, between Insects of insects percent spraying on treated active inand inplants, gredient testing (I) A B G hours 01 aye.-. g f z zf' 24 O 3brs 100.0 100.0 100.0 100.0 5 days... 83. 3 89.8 100. 0 94. 5

. ays-.. D0 48 01 5d 988 1000 1000 1000 0.05 5 days. 93. 3 100. 0 100. 0 100.0 3 hrs. 100. 0 100. 0 100. 0 100. 0 lit- 23'3 82% it; 8""; ys... 8. Meaom 24 3111's--.. 100.0 100.0 100.0 100.0 0.05 1 day 100. 0 98. 3 100. 0 100. 0 5 days... 63. 0 96.1 96. 7 98. 0 D0 48 0.1 5 days." 98.0 98 0 100.0 100.0 0. 05 5 days... 87.0 100. 0 100. 0 100. 0

PLANTS TREATED ON SOIL Period of Coucen- Interval Percentage Mortalities exposure tratlon, between insects of insects percent treating on treated active inand inplants, gredient testing, (I) A B 0 hours days 28.7 73.8 57.7 g filf f 24 M2 00.7 85.5 00.1

M'egoura viciae. 24 0.02 Do 48 0. 02 100. 0 06. 8 100. 0

Table 2 tion onto the soil. The plants were infested after treat- COMPOUNDS (1), A, B AND C AGAINST PEA APHIS Sugar Pea seedlings, 23 inches high, were treated by pouring 10 ml. solution on to the soil. The plants were infested at intervals after treatment with Acyrthosiphon ment with Tetranychus telarius confined in glass rings waxed on to the leaves. Two replications mites) for each treatment with French beans, and one replication (10 mites) with Capsicum.

Time of Concen- Interval Percentage Mortallties exposure trat-ion, between Plants Treatment of mites percent treating Water on plants, active inand (D A B C hours gredient infesting U 0 hrs- 100. 0 100. 0 100. 0 100. 0 0 Capsicum annuum Spray 24 {3 days... 100.0 100.0 100.0 80.0 0 Soil treatment... 24 0.02 1 day 22. 2 20. 0 10.0 27. 3 0 24 0 1 {0 hrs 100.0 100.0 100.0 05.0 0 a days 70. 0 100. 0 100. 0 00. 0 0 French bean 24 0. 02 1 day- 20. 4 16.6 31. 2 20. 4 5. 0

24 0.1 1 day- 100. 0 100. 0 100. 0 100. 0 0 24 0. 05 1 day 00.0 90. 0 100. 0 05. 0 48 0.1 3 days 100. 0 100. 0 100. 0 100. 0 0 48 0.02 1 gay 55.6 188.0 00. 86.3 23.0

s ray 48 0.1 a ays. 100.0 0 .0 00. 10 French bean {Sgiltreatment 48 0.02 1day 52.0 50.0 81.2 70.6 22.2

pisum. Four replications for each treatment with (I) REMARKS and eight replications each for the other treatments. h compounds tested are ll l bl i water except About 25 insects on each plant.

Time of Coucen- Interval Percentage Mortalities exposure of tration, between insects on percent treating Water treated active and inplants ingredient testing, (I) A B G 1 days 1 66.; 0 66. 62. 7 5 .o 24 ms s 30.0 42.8 58.9 40.5 9.2 13 31. S 28. 9 38. 9 17. 4 5. 5 1 02.3 g 9?. 5 5 9. g G 8 8 .0 .1 l0. m s 80.8 78.7 86.0 m4 16.8 13 64. 6 50. 0 65. 5 28. 5 l0. 9

Table 3 COMPOUNDS (I), A, B AND C AGAINST BED SPIDER Capsicum annuum plants, with six to eight leaves, and French bean seedlings, with two leaves, were treated either: (a) by spraying, or (b) by pouring 10 ml. solucompound (1). Solutions were made up as follows:

I 0.2 ml. insecticide were dissolved in 50 ml. of acetone and the solution was made up to ml. with a solution of 0.05% of an emulsifier in distilled water. Further dilutions were made where necessary with the 0.05% emulsifier solution.

The tables show new Compounds A, B and C to be excellent persistent systemic insecticides against aphids and red spiders. They show further that the new compounds, although similar in some respects to the known compound (I), differ from it in their biological behaviour by giving better results as sprays.

The three new compounds are biologically hardly distinguishable from each other.

What we claim is:

' 1. New chemical compounds being sulphoxides ofthe general formula:

g 0 easing-L41" where R, R and R are each an alkyl group containing not more than four carbon atoms.

2. New chemical compounds according to claim 1, where R, R and R in the general formula are each an alkyl group containing not more than three carbon atoms.

3. Pesticides containing a new chemical compound of the general formula:

R0 0 RO/ s-(c:H4) -R" where R, R and R" are each an alkyl group containing not more than four carbon atoms.

4. Pesticides according to claim 1, where R, R and R" in the general formula are each an alkyl group containing not more than three carbon atoms.

5. As a new chemical compound: 0,0-diethyl-S-(ethylsulphinyl)-ethyl thiophosphate,

6. As a new chemical compound: 0,0-dimethyl-S- (methylsulphinyl)-ethyl thiophosphate,

7. As a new chemical compound: 0,0-dimethyl-S- (ethylsulphinyl)-ethyl thiophosphate,

10 8. A process for the production of sulphoxides, wherein a compound of the general formula:

where R, R and R" are each an alkyl group containing not more than four carbon atoms, is treated under neutral conditions with aqueous hydrogen peroxide at not more than moderately elevated temperature to cause an oxygen atom to be added to a sulphur atom of the said compound. v

9. A process according to claim 8, where R, R and R" in the general formula are each an alkyl group containing not more than three carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS 2,140,608 Ufer Dec. 20, 1938 2,560,049 Cook July 10, 1951 2,560,050 Cook July 10, 1951 2,571,989 Schrader Oct. 16, 1951 FOREIGN PATENTS 871,448 Germany Mar. 23, 1953 

1. NEW CHEMICAL COMPOUNDS BEING SULPHOXIDES OF THE GENERAL FORMULA: 